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8/10/2019 course4ppt

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Factors Affecting Completion &

Workover designA) Objectives.

B) Outline.

Major Reservoir Features.

Rock and Fluid Properties.

Fluid Flow. Productivity Index & Inflow Performance.

Drive Mechanism.

Data Collection, Analysis.


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Major Features Of Reservoirs

Sediments, Porosity and Permeability.

Hydrocarbon formation and movement.

Types of traps:

Structural. Folds, Faults, Dome intrusion.

Stratigraphic. Sand lenses, Unconformity.

Contour Maps.


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Reservoir Rock Properties

Matrix

Porosity, Effective porosity

Permeability, Relative permeability.

Fluid saturation

Wettability, interfacial tension & capillarity Fluid distribution in pore spaces.

Reservoir pressure & Bottom hole flowing

pressure


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Reservoir Fluid Properties

Hydrocarbons components.

Phase behavior overview

PVT effects, definition of terms.

Compressibility of rocks and fluid

Formation volume factors Viscosity

Guidelines for sampling using fluid data


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Fluid Flow Through Porous

Rocks Flow concepts: Fluid type, Geometry, State

of Flow.

Darcys Low

Skin effects, partial penetration, perforation

Horizontal/Vertical permeability variation

Productivity index

Well inflow performance


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Reservoir drive mechanism

Introduction

Depletion drive

Black oil, Dry gas, Condensate

Water drive mechanism

Exploitation schemes to utilize drivesSolution gas, Gas cap, Water drive

Geologic factors, layering, fingering

Reservoir pressure.


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II Well Completions

Introduction

The organization is as follows:

1 Design consideration-Completion definition

2 Basic completion types-Configurations

3 Tubing design factors- Inflow performance,tubing size, weight and coupling

4 Effect of drilling practices- Limitations


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Definition of Completion

The completion phase starts when:

The hole drilled to T.D.

Casing cemented in place and any

un-cemented liner landed

A flanged connection on the casing withwhich to install the wellhead

It is proper to assume that the completion

begins when the bit drills the first foot of

the roductive zone.


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Well Planning

Design is critical in new fields

The modern technology should be taken into

consideration to improve any new

completions.

Drilling/Completion design procedure

To estimate the tubing size, proceed with

the following:

1- Test reservoir with drill stem tests.


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Well Planning (Cont.)

2-Consider the necessary restriction added by

casing-cement and perforations, and the

effect of sand control if required

3-Consider the necessary restriction of a

constant flow line back pressure.

4-Consider the pressure loss of tubing frictionbetween formation and surface.

5-Design the production string with required

accessories.


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Well Planning (Cont.)

6-Design casing program to allow installation

of optimum tubing string.

7-Predict the setting depth of all casing

elements.

8-Select optimum bit sizes to allow proper

cementing.

9-Consider material availability, logistics, and

service company limitation.

10-Prepare well prognosis.


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Inflow systems

Illustration of inflow and outflow systems.

Three categories of inflow system.

1- Open hole completions

Advantage and disadvantages

Open hole gravel pack.2- Uncemented, perforated lineres

Advantage and disadvantages


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Inflow systems (Cont.)

3- Cased and perforated wells.

Why it is widespread?

Need for optimum cementing

The perforating process

Limitations for sand control


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Outflow systems

Single Completion with tubing

- Used for wells produced by Sucker rodpumps. The tubing hanging in the well with

pump landing nipple.

- The producing fluid level must be above the

pump level.

- The open annulus allows gas to escape to

minimize gas lock.


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Outflow systems (Cont.)

- Chemicals can be pumped from annulus

Problems:

- Tubing movement with pumping strokes.

- Associated casing and tubing wear.


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Single strings with Packers.

- Used to isolate weak or leaking casing.- Used to isolate casing since its Burst

strength may be not enough to handle shut

in pressure.

- Used in injection and disposal wells to

protect annulus.

- annulus is filled with protective packer fluid


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Permanent Completions

- Packer should contain rugged slips,elastomer seal and seal bore

- Tubing would contain seal assemply at the

end.

Installation procedure

Seal bore packers and PBRs

Tubing movement considerations


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Parallel and Concentric Strings

It is commonly used to- inject chemicals into production string at

bottom of the well

- deliver kill fluids deep in the well to controlgas wells

Multible Completions. Single string: isolated/commingled


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Parallel duals

PBR and Packer application

Tripple Completion

Tubingless Completions

Concept and limitations Macaroni strings, Multiple Completion


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Tubing Design Factors

Definition, Applications of tubing

Using inflow potential to size tubing

- Tubing selection chart

- Effect of gas weight, friction, surface

pressure.- IPR from Darcys equation

- Estimating gas column weight

- Friction loss in tubing


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- Calculation procedure

- Data for example calculation

- Perforation restriction effect

Tubing weight, grade selection

The expected tension, burst and collapseduring well life must be taken into

consideration with design safety factor


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Coupling selection/Consideration

Sealing, Recesses, Strength, Metallurgy,

Handling, Make up.


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Haw drilling practices affect

completions Surface/intermediate hole problems

- Change in casing program

- Inability to cement properly

- Casing wear

- Deviation problems, Dog-Leg


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Haw drilling practices affect

completions Drilling problems in producing zone

- Permeability impairment

- Inadequate formation evaluation

- Poor cementing

- Perforating limitations- Inadequate communication, cooperation


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Workover Planning and Problem

Recognition Objective:

The major points to be described

- What cause abnormal production

- How to test new well performance to

evaluate completion efficiency

- When is a well depleted

- What causes mechanical problems.


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Recognition Definition of Servicing and Workover

- Function of service units & Workover rigs

- Categories of workover

Any work after evaluating the performance of

initial completion

Formation modification or treating

Equipment modification or repairing

Recompletion - Any services requires killing


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Recognition Workover Planning

- Authority of expenditure (AFE)Technical support for recommended action,

Proposed procedure and Estimated cost

- Indications of problemsArtificial lift equipment failure, Rapid

decline, Inadequate completion, Depletion

and Mechanical failure


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Rapid production decline

The production decline curves is the most

common tool to analyze wells behavior to

spot workover candidatesThe possible problem causes are

-Near wellbore permeability loss

Fracture closure, Compaction, Sand grain

Shifting, Fine Migration, Scale deposition,

and Relative permeability effects


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Restriction by sand fill

When sand inters wellbore, it will sittle

down if the velocity is not enough to be

produced. When it is packed in wellbore, it

will reduce the vertical permeability of

flow. It can be bailed or washed out usingwireline, clean fluids or Nitrogen.


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Sand control Failure causes

- Improper installation

* The gravel and screen slots were too large

* Gravel was not completely packed around

screen to protect it from high velocity fluid

inflow.

- Perforation tunnel plugging


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Water or gas coning or fingering

In reservoirs containing water and the

movement of water is bottom water rise, the

critical rate should be calculated and not

exceeded to prevent water coning.

In gas cap reservoirs, the same thing should

be conducted to avoid gas production and

increase GOR.


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A workover may be conducted in such cases

to isolate water or gas entry such as cement

squeeze, plug backs and liner installation.

Communication between zones.

- Need for zone isolation. It is necessary to:

Prevent unwanted gas or water production

Prevent injected fluid from going out of zone

Isolate treatments to the intended zone.


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Poor cement Placement.

- Mud channels through cement sheath

- Poor pipe-to cement bonding (micro

annulus)

- Porous and permeable cement

Cement bonding considerations

Cement bond log - Channeled cement may

create problems in later production life


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Special problems in Enhanced

recovery

- Sever emulsion formation

- Gas or steam locking of pumps

- Sand dissolution by hot water in gravel

packs.

- Chemical precipitation, scaling or bacteria

build up from injected wells


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Tubing,Casing, Packer leaks

The string can fail during operation due to

- Corrosion pitting

- Coupling parting due to backoff

- Rod wear- Tubing wear and corrosion

- Pressure effects (Burst, Collapse)


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Poor initial performanceFirst, the productivity index should be

predicted from the wells data and possible

well testing survey.

The causes of low performanceare:

- Permeability impairment by particle

invasion.

- Clay swelling and dispersion


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- Plugged perforations

Other problems that limit completion success:

- Inaccurate formation evaluation

- Ineffective stimulation, cleanout

- Improper start up program

- Poor tubing design

- Channeled cement

- Poor sand control design


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Depletion.- The economic limit

It is vary greatly based on oil price and

production rate

- Reservoir behaviorRate Vs time production or Vs cumulative


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Mechanical problems:- Annulus pressure build up

Packer leak, Sleeve leak, Wellhead seal

failure.

- Sand flowGravel pack failure, screen erosion, casing

leak, collapsed casing, cement failure,

compaction.


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A workover may be conducted in such cases

to isolate water or gas entry such as cement

squeeze, plug backs and liner installation.

Communication between zones.

- Need for zone isolation. It is necessary to:

Prevent unwanted gas or water production

Prevent injected fluid from going out of zone

Isolate treatments to the intended zone.


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- Excessive gas or water production

Tubing leak, Casing leak, Cement failure,

breakthrough from injector.


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Types of workover operations

Stimulation

Hydraulic Fracturing

- Fracture orientation Vs depth

- Application of proppant, acid etching

- Basic fluid additives- Job design, field operations

Acidizing

- Design considerations for sandstone


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- Carbonate need additional flow channels

- Field operation, inhibition

Chemical Stimulation

- Objective

- Rock wettability factorSome things shoul be avoided

- Pumping large amount of untreated water

- Using fresh water for overflush


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Workovers involving drilling- Deepining an existing well to new zone

- Underreaming for gravel packing application

- Milling out casing

Swabbing in after well work- Nitrogen injection

- Under balanced perforating,back surging

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